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Nikola Tesla stated in his patent, Art of Transmitting Electrical Energy Through Natural Medium, that he used sensitive instruments to measure lightning discharges:

In the course of certain investigations which I carried on for the purpose of studying the effects of lightning discharges upon the electrical condition of the earth I observed that sensitive receiving instruments arranged so as to be capable of responding to electrical disturbances created by the discharges at times failed to respond when they should have done so, and upon inquiring into the causes of this unexpected behavior I discovered it to be due to the character of the electrical waves which were produced in the earth by the lightning discharges and which had nodal regions following at definite distances the shifting source of the disturbances. From data obtained in a large number of observations of the maxima and minima of these waves I found their length to vary approximately from twenty-five to seventy kilometers, and these results and certain theoretical deductions led me to the conclusion that waves of this kind may be propagated in all directions over the globe and that they may be of still more widely differing lengths, the extreme limits being imposed by the physical dimensions and properties of the earth.

Does anyone knows of such method of measurement? How does it work? Did anyone else ever get the same results as Nikola Tesla? Is it possible with modern instruments and methods to measure electrical waves produced by lightning?

SamGibson
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Marino Klisovich
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  • there's no "electrical waves"; there's *electromagnetic waves*, and "electrical disturbances" are what was observed, i.e. disturbed operation of electrical devices. Wording is important, here! – Marcus Müller Apr 28 '19 at 13:32
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    Tesla used a less rich terminology. He calls the whole magnetic phenomena 'magnetism'. But what's interesting is if this natural earth-electric-waves produced by lightning discharges exist. If they do, then the next natural step is to make a device that can generate such waves. – Marino Klisovich Apr 28 '19 at 17:40
  • that device exists. It's called a "spark plug" and every gasoline-driven car has several. Larger ones exist as overvoltage protection in larger electrical substations. There's really nothing special going on about lightning here - it's just an electrical spark. – Marcus Müller Apr 28 '19 at 18:07
  • in fact, the German word for "doing a radio transmission" is "funken", which means "to spark", because early radio transmitters were exactly that: spark gaps "fired" to cause broadband EM waves. Heinrich Hertz used these to demonstrate the existence of electromagnetic waves. So, you're only around 140 years late. The method used originally by Hertz, Marconi and Tesla simply are terribly non-selective and inefficient. That's why you've not seen a spark gap transmitter. – Marcus Müller Apr 28 '19 at 18:09
  • Also, please don't call them electric waves. Just because Tesla did doesn't mean it's right. These aren't electric waves, they are electromagnetic waves, and the vocabulary for these existed at least 45 years prior to this patent. Compare: Maxwell, Hertz. (in fact, the patent even calls them "hertzian electro-magnetic waves") – Marcus Müller Apr 28 '19 at 18:12
  • They only used them to transmit a relatively low energy signals. Tesla said he created a device which waves that superseded those created by lightning. IMHO, you only need to hit the ground with high-energy lightning at rates of 5-12 kHz. – Marino Klisovich Apr 28 '19 at 18:29
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    Tesla was a little crazy in his later years regarding wireless power transfer, just as a side note. You really overestimate what Tesla did more than 100 years ago. A 12 kHz radio transmitter isn't anything that you'd have to invent. It's called long wave radio broadcasting, and the world has been doing it for a long time. And no, they don't do it with lightning, because that's inefficient. They use antennas. As a side effect, you can have different signals on different frequencies that don't disturb each others instead of just one transmitter wasting the spectrum for everybody. – Marcus Müller Apr 28 '19 at 18:39
  • (spark gap transmitters is really what you're describing here. We don't use them anymore, haven't done so for more than 100 years, because of the fact that they don't produce a nice signal, just wideband noise, so that everyone interferes with everyone. Really, there's nothing magical that Tesla did and the modern world couldn't reproduce in a garage. and to repeat it: making a spark to generate a wave is inefficient, due to the high losses in the arc. Which is pretty obvious by the fact that that spark glows white!) – Marcus Müller Apr 28 '19 at 18:42
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    Not a full answer, but you may be interested in [the AMS AS3935](https://www.digikey.com/catalog/en/partgroup/as3935-demo-kit/30482) -- a microchip specifically designed to detect lightning activity. –  Apr 29 '19 at 02:41

3 Answers3

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sensitive receiving instruments arranged so as to be capable of responding to electrical disturbances created by the discharges

A lightning strike is an enormous current flowing for very shortly. That (thanks to Ampere and Maxwell) we know to induce an electromagnetic wave with a very high bandwidth and very high power.

So, any radio receiver these days is more than capable of "detecting" such discharges (simply by malfunctioning for a short time).

What Tesla had was probably even simpler: Close enough to the discharge, the change in E-Field might be drastic enough to simply make a spark gap across a simple coil spark.

Really, what about googling "lighning detection"? There's large-scale citizen science projects where people contribute their own lightning counts to a large central database.

Marcus Müller
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  • I think it is less about detecting lightning at all (which is trivial) and more about detecting the resonances which Tesla mentioned. The resonances which correspond to 25 to 70km wavelengths. – JRE Apr 29 '19 at 10:43
  • hm, but these resonances would still be easy to pick up with any E-field probe and regular sampling. – Marcus Müller Apr 29 '19 at 11:25
  • In his patent Tesla describes the device that was used used for detecting ground-electric-waves. It is shown on figure 2. – Marino Klisovich Apr 29 '19 at 11:39
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It is entirely possible to detect lighting strikes with modern (and not so modern) equipment.

Any AM receiver will "detect" lightning strikes. There are also electrometers which can detect strikes as well as the conditions before the strike actually occurs.

Standing waves caused by resonance should also be detectable.

A lightning strike causes a very broadband burst of radio waves. It should cause radio waves in (nearly) equal intensity up to very high frequencies (GHz and beyond.)

It should be possible to use a spectrum analyser on the RF received from a lightning strike. Resonances would show up as peaks at particular frequencies, absorption would show up as dips.

The frequencies are very low, though. Perhaps lower than most RF equipment is designed for.

The patent you link to refers to resonances between wavelengths of 25 to 70 kilometers. That means frequencies between 4.3 kHz (70 km) to 12 kHz (25 km.)

Those are more typically associated with audio frequencies.

This makes an intersting experiment possible:

  1. Use a long wire and a ground wire to receive the signals. A small amplifier may be needed, may be not.

  2. Connect the long wire and the ground to the microphone input on the sound card of your PC

  3. Record typical noise when there is no known thunderstorm in your area.

  4. Record typical noise when there is a thunderstorm in progress.

  5. Compare the spectrums of the two different recordings, and look for peaks or dips during the thunderstorm.

Lightning strikes in the recordings should be visible as "spikes" in the waveform view, and as broadband increases in the spectrum view.

If the peaks are too weak to clearly see, then you may need an amplifier and maybe impedance matching to get more of a signal from your antenna. The amplifier should be fairly undemanding - a JFET preamplifier as commonly seen for microphones should work well.

It should be fairly easy to build and use such a setup. Just a couple of wires, a PC, and some common software. Audacity would work, or Baudline. I'm sure there are many others.

I'd personally use Baudline, and the cross correlation function to compare the recordings.

You could also write your own software, but it is probably better to see what you can do with the available software before you write your own.

Given that Tesla could find the resonances with the (relatively) crude measuring equipment available in his time, they ought to be fairly easy to detect with modern analysis methods.

The above ignores the safety aspects of connecting an antenna and ground to your PC. That's a seperate problem. A long wire pointed upwards during a thunderstorm is basically an invitation for lightning to strike.

If your house has lightning protection, and your antenna is fairly small, then it should be safe enough - the rabbit ears antenna on a portable radio doesn't attract lightning.

A really long wire that stretched from your house a couple of hundred feet up will attract lightning.

Radio amateur operators have equipment for dealing with that kind of problem, so there are solutions available.

For beginning experiments, though, a small antenna should be safe enough and adequate to see if you want to continue.

Note that you are not building an AM receiver. You are just picking up and digitizing the "RF" as it is. No diodes are needed.

JRE
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  • Thank you for comprehensive answer. This means Tesla's resonant transformer (Tesla coil) was tuned to frequencies of 5-12 kHz. I don't think any TC enthusiasts are aware of this. Tesla also says that measured electric waves traveled through earth (not through air as we think). – Marino Klisovich Apr 28 '19 at 17:06
  • It means the one he used to detect lightning resonances was tuned to that range. It doesn't necessarily mean that the ones he used to generate high voltage were tuned to that range. – JRE Apr 28 '19 at 17:09
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    Electromagnetic waves do both. And, there are power systems that use the Earth as part of the power distribution. – JRE Apr 28 '19 at 17:10
  • What kind of power systems are that? – Marino Klisovich Apr 28 '19 at 17:11
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    Also remember that while Tesla was a genius, he was a.) fookin nuts and b.) held ideas about physics that were known to be wrong during his lifetime. – JRE Apr 28 '19 at 17:12
  • I'm only interested in his original patents are practical results. – Marino Klisovich Apr 28 '19 at 17:12
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    [Single wire, earth return.](https://en.wikipedia.org/wiki/Single-wire_earth_return) – JRE Apr 28 '19 at 17:13
  • Wow, what a surprise! – Marino Klisovich Apr 28 '19 at 17:23
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The frequencies in question are classified as very low frequency (VLF). They are used for communication with submarines. Historically, VLF was used for some wireless telegraphy applications. For additional information you can read the very low frequency Wikipedia article and the references listed there. There are also lower frequency bands called ultra low frequency and extremely low frequency.